1. Field of the Invention
The present invention relates to a printer which prints using a print head mounted on a movable carriage, such as an ink jet printer, which prints through uni-directional or reciprocal back and forth motions of its print head carriage. More particularly, the invention relates to such a printer in which carriage speed non-uniformities are accommodated by determining print direction and print speed based on printed data content, paper size and the like.
2. Description of the Related Art
Printers such as ink jet printers have become an extremely popular format for achieving high quality computer print out at low cost. These printers form a printed image through movement of a movable carriage, on which a print head is mounted, in reciprocal uni-directional or left and right printing passes at high scanning speeds across the width of a recording medium, while the recording medium is slowly fed in the lengthwise direction. In the case of ink jet printers, the printed image is formed by ejecting small ink droplets from the print head in predetermined patterns on to the recording medium.
One impediment to the formation of high quality images is non-uniformities in carriage speed. A particularly troublesome source of carriage speed non-uniformities is overshoot and ringing in carriage speed which occurs as the carriage is ramped up from a standstill position to a target scanning speed. This situation is illustrated in FIG. 1, in connection with a printer having two print heads, labeled xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d, mounted on a single moveable carriage 11. FIG. 1 is a graphical representation of carriage speed 12 as the carriage commences movement from a standstill position at 14 to a target scanning speed 15 across the width of a recording medium. As seen in FIG. 1, during ramp up from a standstill position to a target scanning speed, speed in carriage 11 exhibits ringing and overshoot indicated generally at 16.
Assuming that print head A commences print out at the position indicated by xe2x80x9caxe2x80x9d, it will be seen that print quality from print head A will be affected by carriage speed non-uniformities to the extent indicated at xcex94A. On the other hand, print head B will not reach position xe2x80x9caxe2x80x9d until the carriage has continued movement to the position indicated in phantom lines. At that position, ringing, overshoot and other carriage non-uniformities have decreased greatly. Accordingly, print quality from print head B will be affected by carriage speed non-uniformities only to the extent of that indicated at xcex94B. Since xcex94A and xcex94B are different, it will be appreciated that print quality will be affected differently for print head A and print head B. Thus, in a case where print out by print head A is desired to be superimposed over print out by print head B, accuracy of the superimposition will be degraded, since at the same print position, print head A will be printing at a slightly different speed than print head B.
Some conventional devices have avoided this effect on print quality by printing with the outermost print head in forward and reverse directions, that is printing only with print head B in a forward direction and printing only with print head A in a reverse direction. With this arrangement, the carriage will have reached a stable enough constant speed in each direction by the time that print out from each head is effected. On the other hand, this arrangement slows overall printing efficiency, since it is not possible to print with both heads in each of the forward and reverse directions.
Another problem caused by carriage speed non-uniformities is illustrated in FIG. 2, and involves coordination of forward and reverse printing. Shown in FIG. 2 is a recording medium 20 on which it is desired print a first band of print data in area 21 in a forward direction, followed by a second band of print data in a reverse direction in band 22. 24 indicates overshoot and ringing in carriage speed in the forward direction of printing, while 25 indicates carriage speed overshoot and ringing while printing in the reverse direction. As can be seen in FIG. 2, carriage speed matches only in the central region 26 in each of bands 21 and 22. At the left most position 27, while carriage speed in reverse printing is constant, significant overshoot and ringing is still exhibited for printing in the forward direction; likewise, at extreme right position 28, although carriage speed in the forward direction is constant, significant ringing and overshoot is still exhibited in carriage speed in the reverse direction. Accordingly, print out at the extreme right and extreme left positions does not match in vertically adjacent bands, resulting in degraded print quality.
It is an object of the invention to address carriage speed non-uniformities, by providing for a judgment of printing direction and/or printing speed based on content of print data, recording medium width, and the like.
In one aspect, after commencing print out in one direction, a determination is made prior to each subsequent scan as to whether or not the lateral extent of the printed data is great enough so as to cause degradations in print quality, due to non-uniformities in carriage speed, if the subsequent scan were printed in a reverse direction. For example, if a first scan were printed in a forward direction, and included print data which extended across the entire width of the recording medium, and a subsequent scan includes print data that also extends across the entire width of the recording medium, than a determination would be made that print quality would be adversely affected by printing the subsequent scan in the reverse direction. Accordingly, the subsequent scan is printed in the same forward direction as the first scan. On the other hand, if the subsequent scan included print data only in a central area of the recording medium, then print quality would not be adversely affected by non-uniformities in carriage speed. Accordingly, reverse printing of the subsequent scan would be effected. Thereafter, printing for a next subsequent scan could be effected in either of the forward or reverse directions, regardless of the content of the print data, since the now-previous scan occupies only a central area of the recording medium indicating that carriage non-uniformities would not adversely affect print quality of the next subsequent scan.
Likewise, if print out were being effected on a narrow-width recording medium, occupying only a central area of carriage scanning, then printing could be effected in either a forward or reverse direction without adversely affecting print quality due to carriage speed non-uniformities.
In further aspects, the invention slows the overall carriage printing speed for individual ones of printing scans, so as to lower the adverse effect of carriage speed non-uniformities. Specifically, at slowed carriage scanning speeds, the size of ringing and overshoot non-uniformities are reduced significantly. Accordingly, even though one or two printing scans on a recording medium might have been performed slowly, overall printing efficiency is increased since other scans can be printed in forward and reverse directions, without adversely affecting print quality due to carriage speed non-uniformities. Accordingly, overall printing efficiency is increased.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of preferred embodiments thereof in connection with the attached drawings.